Studies with both rats and nonhuman primates demonstrate that sex can be an important vulnerability factor for cocaine abuse. Females are more sensitive than males to the reinforcing effects of drugs. Estrogen, in particular, may play an important role in modulating the reinforcing and locomotor activating effects of psychomotor stimulants. An additional factor in the vulnerability to initiate drug self-administration is stress. We hypothesize that estrogen, stress and cocaine converge to activate the dopamine-regulated molecule DARPP32, and that this underlies the enhanced vulnerability to behavioral effects of cocaine seen in female animals. This may also increase the risk of female animals to stress-induced relapse to cocaine selfadministration. In Specific Aim 1 we will identify interactions between sex, stress, and ovarian hormones on acquisition of cocaine self-administration. The effect of maternal separation stress on acquisition of cocaine self-administration will be compared in male and female rats and in ovariectomized females with and without estrogen replacement. An additional goal of this study is to explore the molecular neuroadaptations that underlie the effects sex, estrogen, and stress on cocaine self administration. Cocaine increases synaptic dopamine, which acts at D1 receptors, leading to phosphorlyation and activation of DARPP32, an inhibitor of protein phosphatase 1, by PKA. This signaling pathway is critical for modulating both the reinforcing properties of drugs of abuse and the persistent neuroadaptations associated with cocaine exposure, stress and estrogen treatment. In Aim 2 we will investigate whether sex and ovarian hormones modulate cocaine self administration through activation of the DARPP-32 signaling pathway. Although DARPP-32 is critical for the reinforcing properties of cocaine in male mice, it is unknown whether this is influenced by sex, estrogen or stress. In Aim 3, genetic manipulation of DARPP-32 will be used to examine the ability of this molecule to modulate the effects of sex, estrogen, and stress hormones on the rewarding properties of cocaine using knockout mice that lack either DARPP32 or its homologue I-1. It is hypothesized that female mice lacking DARPP-32 or I-1 may show a greater attenuation in the behavioral properties of cocaine than males. These experiments are of great significance for women's health since they may help to identify a molecular mechanism underlying the convergent behavioral effects of cocaine, estrogen and stress and thus lead to novel treatment strategies for cocaine abuse in women.